Annual Maximum Rainfall Trends in Canada - Environment Canada Engineering Climate Datasets v3.10 Update

A recent post ( reviewed trends in annual maximum rainfall, their direction and statistical significance (i.e., showing whether the trends strong or are mild and just reflect normal variations).

Now there is an update. Environment and Climate Change Canada has just released v3.10 of the Engineering Climate Datasets that include annual maximum series data used to derive IDF curves, as well as the trends in those annual maximum series.  (note: trend data are contained in the comma delimited text file idf_v-3.10_2020_03_27_trends.txt in the file on the Environment Canada download site).

Overall many additional stations have been added to the trend analysis.  Version 2.30 had 565 stations, Version 3.00 had 596 station and Version 3.10 now has 651 station.  The average length of record is 25.5 years.  How have the trends in annual maximum rainfall changed? The 3 charts below show that the change is very gradual, there are more significant increases than decreases, but overall the percentage of non-significant trends is unchanged.

Annual Maximum Rainfall Trends in Canada Environment Canada Engineering Climate Datsets
Maximum Rainfall Trends in Canada - Engineering Climate Datasets v3.10, v3.00 and v2.30, Environment and Climate Change Canada
The summaries at the bottom show:

Trend in Maximum Rain   v3.10        v3.00         v2.30
Significant Increase            4.28%      4.18%        4.09%
Significant Decrease           2.24%      2.33%        2.30%
No Significant Trend        85.80%     85.55%      86.37%
No Calculation                    7.68%      7.94%        7.24%

How about regional trends? Some provinces have more decreases than increases:

annual maximum rainfall environment canada data trends
Annual Maximum Rainfall Trends in Canada, by Province / Region - Environment and Climate Change Canada Engineering Climate Datasets v3.10 (March 2020)

Trends in the Toronto area are shown on the following charts for the City of Toronto, City of Mississauga (Pearson Airport), and City of Markham (Buttonville Airport).

City of Toronto Annual Maximum Rainfall Environment Canada
Toronto Maximum Rainfall
City of Mississauga Annual Maximum Rainfall Environment Canada
Mississauga Maximum Rainfall

Markham York Region Maximum Rainfall Annual Maximum Rainfall
Markham, York Region Maximum Rainfall

Trends in Toronto indicate annual maximum rainfall is decreasing for all durations from 5 minutes to 24 hours.  The decrease for the 12 hour duration is statistically significant.

Trends in Mississauga at Pearson Airport are decreasing for most durations, however the 1 hour duration trend is increasing due to the July 8, 2013 peak.  No Mississauga trends are significant.

Trends in Markham, in southern York Region are decreasing for shorter durations of 30 minutes or less and increasing for longer durations. None of the trends are significant.


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